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2017, The Year in Paleontology

2017 is at an end. While the year has had a lot of things that will make us say good riddance, the year in paleontology was extraordinary. To give you an idea of just how extraordinary, let’s look at what has been discovered. Far too much has gone on, so we can’t look at everything, but if we just look at the new species that have been published, it will give us a decent proxy. Using that as a measure, what a year it has been.

111 angiosperms (flowering plants). One new species is Foveomonocolpites ravnifossil pollen from the early Cretaceous of Isreal.

7 Gingoales, 20  conifers, 27 other seed plants. and 55 other plant fossils, and this doesn’t even include 4 new red algae, one of which is Rafatazmia chitrakootensis from Indiathe oldest known plant fossil at 1.6 billion years old.

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23 cnidarians. including this jellyfish from the Cambrian.

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68 bryozoans and 56 brachiopods,

48 echinoderms,

82 malacostracans (crabs), 87 ostracods, and 9 other crustaceans

112 coleopterans, 2 dermapterans, 1 dictyopterans, 50 dipterans, 20 hemipterans, 47 hymenopterans, 5 mecopterans, 22 neuropterans, 25 odonates, 10 trichopterans, and 44 other insects

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A fungus gnat trapped in amber some 45-55 million years ago is carrying on the upper portion of its severed leg a pollen sac from an orchid – the oldest evidence of the flower ever discovered. Credit: Oregon State University
Read more at: https://phys.org/news/2017-05-evidence-oldest-orchid-fossil.html#jCp

72 arachnids, 32 trilobites and 33 other arthropods

79 ammonoids and 31 other cephalopods, 140 gastropods, 71 bivalves, and 11 other molluscs

42 conodonts, 1 early jawless vertebrate, 5 placoderms, 22 sharks and their relatives, and 102 bony fish

3 temnospondyls, 3 lissamphibians, and 2 other amphibians

4 rhynchocephalians, 12 other lizards and snakes, including this one named after Neil Gaiman and this Antarctic mosasaur, 3 icthyosaurs, and 8 sauropterygians (Mesozoic marine reptiles).

12 turtles, 9 crocodilians,

42 nonavian dinosaurs, including 9 ornithischians (including Zuul, the destroyer of shins and the most complete ankylosaur), 21 theropods,  and 12 sauropods.

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20 birds, 6 pterosaurs, 1 basal archosauriform named Teleocrater, and 3 other reptiles.

11 non-mammalian synapsids, 5 metatherians, 10 xenarthrans, 1 elephant, 4 sirens (dugongs and manatees), 5 bats, 25 ungulates, 14 cetaceans, 11 carnivorans, 6 lagomorphs (rabbits and hares), 66 rodents, 6 primates, 20 other eutherians, and 6 other mammals.

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The skull of Microwhaitsia. Credit: Huttenlocker and Smith 2017

55 other animals, as well as 54 various other organisms, including foraminfera and others of uncertain affinities.

All told, 2003 new species. So whatever else happened this year, it was a good year for paleontology. Here’s hoping that 2018 is good all the way around.

Buffalo National River: Boone Formation

If you are looking for a great place to begin your canoeing experience, or just a quiet river to float down with great views, you can’t go wrong with the Buffalo National River in Arkansas as it flows through the Ozark and Boston Mountains. In 1972, Congress declared the Buffalo to be a National River, the first river to be so designated in the Unites States, which protects it from industrial use and any construction that might change the natural character of the river. It is renowned for its clean water and spectacular bluffs. People come from all over to camp in the park, hike its trails, and float the river. Much of the river is easy to float, so a welcome adventure for novices, although the upper reaches can be challenging.

buffalo-river-map

This is the first of many posts about the geology of the river and the fossils that can be found in the park. Please note that this is a national park, so collecting fossils within the park boundaries is strictly prohibited. However, many of the formations discussed herein can be found throughout large portions of the Ozarks, so if you want to collect fossils, consult a geologic map and find a road that runs through the formation outside the park to find suitable roadcuts. Fossil collecting is allowed on state land, so just make sure you are not in a national park, national forest, or on someone’s private land (unless you have their permission).

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AGS EWS-7. Stratigraphic column for upper Buffalo River

 

The Buffalo river cuts through several formations which are mostly Ordovician or Mississippian in age (~470 to 320 Mya). You can find geologic maps in pdf format of the Buffalo National River here and here.In the western reaches, the primary formation is the Everton Formation, but in the central and eastern portions of the river, the Boone Formation dominates. There are numerous bluffs displaying thick sections of the Boone.

The United States Geological Survey describes the Boone Formation as “mainly finely crystalline limestone with some cherty limestone and interbedded chert and minor shale. Approximately 400 ft. maximum thickness.” There is a lot of limestone in the Ozarks, but the nodules and thin beds of chert make the Boone stand out from the others.

Copy of boonecave

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It is early Mississippian in age, although exactly how old is a bit debateable. The USGS lists it as being in the Meramecian/Osagean stages, which places it mostly in the Middle Missippian. However, the Arkansas Geological Survey says it is in the Kinderhookian/Osagean stages, which are mostly early Mississippian. These stages are regional North American names, so you won’t find them on standard geological time scales meant to be used globally. At any rate, the Boone formed approximately 340-359 million years ago.

During the Paleozoic Era, the ocean had several cycles of raising and lowering sea levels. During the time the Boone Formation was forming, the region was a near shore marine environment, which explains the limestone and shale. The chert has typically been ascribed a biogenic origin, possibly the result of blooms of diatoms and radiolarians, both of which are single-celled organisms that make shells from silica, rather than the more common calcium carbonate which helped form the limestone. These organisms have also been presumed to form the Arkansas novaculite, a formation of metamorphosed microcrystalline quartz that reaches up to 900 feet in thickness. However, recent work indicates that both the Boone chert and the novaculite were formed from volcanic ash, created by an island-arc volcanic chain that existed about where the Ouachita Mountains are today.

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“Honeycombed” rocks seen along the Buffalo. NPS, Buffalo National River.

 

Northern Arkansas is known for its widespread karst topography, meaning it has a lot of sinkholes and caves, most of which are in the Boone Formation. The cave systems are so extensive that at periods of very low flow, the entire Buffalo River is swallowed up and becomes subterranean in a few areas. The Boone forms the ceiling of the most famous cave in Arkansas, Blanchard Springs Caverns, which are well worth visiting if you find yourself in northwest Arkansas. On a side note, you may find references to the Boone in Blanchard Springs being as young as 310 million years old, but with better refinement of dating techniques and better dating of the rocks, that date has been pushed back.

The next posts in this series will cover the fossils that have been found in the Boone Formation. Stay tuned.

 

 

 

 

National Fossil Day

NFD_-2017_Poster-96dpi-613pxtallToday is National Fossil Day™. The National Park Service holds this annual event on the second Wednesday every year to coincide with Earth Science Week sponsored by the American Geosciences Institute. Earth Science Week highlights the important role of earth sciences in our everyday lives and “to encourage stewardship of the Earth.” National Fossil Day is, as NPS says, “held to highlight the scientific and educational value of paleontology and the importance of preserving fossils for future generations.”

In honor of the day, I am going to give you a whirlwind tour of some of our most outstanding fossils from all over the state. People may not think of Arkansas as being rich in fossils, but we have a rich natural history spanning 500 million years. To give you a quick summary of the wide array of fossils, just check out the map on the fossil page, reproduced below.

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Arkansas Geological Survey regional map, annotated with reported fossils.

The most fossiliferous region in the state is the Ozarks, without a doubt. It is a favorite fossil collecting spot for many people, even though much of the area is national forest or national park owned, which prohibits fossil collecting. Nevertheless, fossils may be collected on any roadcut. I-65 near Leslie has several fossiliferous roadcuts. You are most likely to find abundant examples of crinoids, bryozoans like the screw-shaped Archimedes, clams and brachiopods, ammonoids (mostly goniatites), corals such as horn corals and tabulate corals, as well as the occasional echinoid and trilobite, along with many other types of fossils. This list of fossils makes it plain that the Ozarks are dominated by marine deposits, but you can find the occasional semi-terrestrial deposit loaded with plants like Calamites and Lepidodendron.

Top, left to right: Calamites, spiriferid brachiopod, blastoid echinoderm, goniatite ammonoid. Bottom left to right: Archimedes bryozoan, crinoid with calyx and fronds (very rare, mostly you just find pieces of the stalk).

There are a few fossils that particularly stand out. One is Rayonnoceras, a nautiloid ammonoid, which reached lengths of over two meters, making it one of the longest straight-shelled ammonoids ever found. The other is a shark named Ozarcus. While shark teeth are common, it is rare to find one that preserves parts of the skull and gill supports. At 325 million years, Ozarcus is the oldest one like this ever found and it changed the way we viewed shark evolution, indicating that modern sharks may be an offshoot of bony fish, not the other way around.

bc-067t-lgWe can’t leave the Ozarks without talking about Conard Fissure, a spectacular collection of Pleistocene fossils. Barnum Brown excavated the first chamber of the cave in 1906, pulling out thousands of fossils or all kinds, many of which were new to science. Of course, of all of them, the ones that most people remember were 15 skeletons of Smilodon, the largest of the saber-toothed cats. The one pictured to the right is a cast of one from La Brea, California. All of ours are held at the American Museum of Natural History.

The Ouachita Mountains are not nearly as fossiliferous, but they have two important types of fossils that are commonly found: graptolites (below left) and conodonts (below right, not from AR, Scripto Geologica). Graptolites are thought to be closely related to pterobranchs, which are still living today, even though the graptolites themselves are all from the Paleozoic Era. Most of the time, Graptolites look like pencil marks on slate, but if you find a good one, you can see they are often like serrated files that may come branched or coiled. The reason these are important is because they are hemichordates, the closest group to the chordates, all animals with a spine (either a stiff rod or actual bone). Conodonts, on the other hand, are the closest we have to the earliest vertebrates, looking like nothing so much as a degenerate hagfish.

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The coastal plain is quite fossiliferous and has attracted the majority of press because it is here where you will find Cretaceous aged rocks and that means dinosaurs and their compatriots. Here you will find thousands of Exogyra oysters. Scattered among them, you can find numerous shark teeth, along with teeth from Enchodus, the saber-toothed herring (although not really a herring), especially if you look in the chalk beds. You can also find the rare example of hesperornithids, extinct diving birds, as well as fossil crocodilians.

But of course, the main draws here are the marine reptiles and the dinosaurs. Mosasaur vertebrae are not uncommon, although the skulls are. More rarely, one can find plesiosaur (the article only mentions elasmosaurs, which are a type of plesiosaur, but most plesiosaur fossils in Arkansas cannot be identified that closely) vertebrae as well.And then of course are the dinosaurs. We only have a few bones of one, named Arkansaurus, but we have found thousands of footprints of sauropods, the giant long-necked dinosaurs. Since the sauropods that have been found in Texas and Oklahoma are titanosaurs, such as Sauroposeidon, it is a good bet the footprints were made by titanosaurs. A few tracks have also been found of Acrocanthosaurus, a carnivorous dinosaur like looked something like a ridge-backed T. rex. Acrocanthosaurus reached almost 12 meters, so while T. rex was bigger, it wasn’t bigger by much.

Top left: Mosasaur in UT Austin museum. Top right: Plesiosaur vertebra from southern AR. Middle left: reconstruction of Arkansaurus foot. Middle right: statue of Arkansaurus (out of date). Bottom left: Sauropod footprints. Bottom right: Acrocanthosaurus footprint, Earth Times.

The eastern half of the state is dominated by river deposits from the Mississippi River, so the fossils found there are mainly Pleistocene aged, with the exception of a few earlier Paleogene fossils near Crowley’s Ridge. Pleistocene deposits can be found all over the state, as they are the youngest, but are most common in the east. In these deposits, a number of large fossils have been found. A mammoth was found near  Hazen, but we have almost two dozen mastodons scattered over the state. I already mentioned Smilodon, but we also have  , the giant short-faced bear, dire wolves, giant ground sloths, and even a giant sea snake named Pterosphenus. Most unusual of all is a specimen of Basilosaurus, which despite its name meaning king lizard, was actually one of the first whales. Considering the month, I would be remiss not to include Bootherium, also known as Harlan,s musk ox, or the helmeted musk ox.

Top left: Mastodon on display at Mid-America Museum. Top right: Basilosaurus by Karen Carr. Bottom left: Arctodus simus, Labrea tar pits. Wikipedia. Bottom right: Bootherium, Ohio Historical Society.

This is nowhere near all the fossils that can be found in Arkansas, but it does give a taste of our extensive natural history covering half a billion years. After all, we wouldn’t be the Natural State without a robust natural history. Happy National Fossil Day!

Mystery Fossil Revealed

Monday I posted a set of pictures showing an Arkansas fossil. Were you able to figure it out. Check below for the answer.

This skull and mandible comes from the Madrean Archipelago Biodiversity Assessment (MABA) website. I couldn’t find a good picture of an actual fossil, so I used this modern example instead. Below is a living version.

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Myotis leibii, Eastern small-footed bat. Credit: Gary Peeples/USFWS

The skull is that of Myotis leibii, the eastern small-footed Myotis. Myotis bats are also called mouse-eared bats, the most famous of which is the little brown bat, Myotis lucifugus. The other fossil bat in Arkansas is the big brown bat, which is not in the genus Myotis at all. It is in the genus Eptesicus (E. fuscus specifically).

I have talked about E. fuscus before, where I talked a bit about bats in general. I didn’t go into their phylogeny at all, so I will talk about that here. Bats as a whole belong to the order Chiroptera, which is the sister group to a group called Fereuungulata. That group includes artiodactyls, cetaceans (whales and dolphins), carnivorans, and pangolins. Altogether, Chiroptera and Fereuungulata form the horribly named Scrotifera. Why do I say it is horribly named? Besides the fact that naming such a large group after scrotums is a bit odd, take a look at the simplified mammal phylogeny illustrated by Darren Naish.

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Notice what is NOT in Scrotifera. That’s right. Primates, such as us. Yes, we are more closely related to rats and squirrels than we are to bats, dolphins, or cats and dogs. We are also not included in the group named for a feature we possess.

Both Myotis and Eptesicus are Vesper bats, meaning they belong in the family Vespertilionidae, along with over 300 other bat species. When it comes to diversity, mammals could easily be described as rodents, bats and their less common relatives, seeing as how those two groups include 60% of all mammals. Vesper bats are in the suborder Microchiroptera, the micro bats. The other suborder, Megachiroptera, is composed of the fruit bats like the flying foxes. The two suborders are rather lopsided in numbers, with just under 200 species in Megachiroptera and over 1000 in the Microchiroptera. This is the traditional classification at any rate.

There is another phylogeny that splits it up slightly differently and gives them different names. Megachiroptera has become Yinpterochiroptera and includes the horseshoe bats in the group called Rhinolophoidea as well as the lesser and greater false vampire bats in the genus Megaderma. Everything else that was in Microchiroptera  is in Yangochiroptera.

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You can read more about it here, or in the original paper here.

So returning to the vesper bats, these include most of the bats people are likely to run into, which is why  the bats in this group are sometimes called common bats. Most of the bats in this group have rather plain faces and are insectivores. Myotis leibii itself belongs in the group Myotinae, marked in the red box in the phylogeny below, which was also put together by Darren Naish.

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The interesting thing about this is that Eptesicus, the big brown bat, is in the serotine clade, up near the top of the tree and quite a distance away from Myotis, the little brown bat. Eptesicus is also sometimes called a house bat, but the house bats are in the group Scotophini, which while still in Vespertilioninae, is not closely related within the group. This is part of the reason common names can get confusing. just because the common names are similar and overlap doesn’t necessarily mean they are at all closely related.

M. leibii itself lives in forests throughout eastern North America, in spotty patches from Canada to Arkansas and Georgia. It is a small bat, weighing only about 5 grams and with a wingspan of less than 10 cm. Unusually for its size, it is long lived, living as long as 12 years and tolerates the cold better than most other bats, so spends less time in hibernation than other bats.

The fossil record of M. leibii is sparse, although the fossil record for Myotis in general is fairly good for bats. According to molecular data, the genus Myotis first appeared roughly 16 Mya, with the North American clade splitting off no more than 9 Mya. However, the actual fossil data indicates Myotis is far older, with the earliest known Myotis fossil being 33 Mya to the earliest Oligocene, although in North America, the record only extends to the late Miocene no more than 23 Mya. Interestingly, the fossil record for M leibii demonstrates a range far greater than the current distribution, with fossils being found as far as Oregon. In Arkansas, fossils are limited to one spot, which happens to be the same spot Eptesicus has been found: pleistocene deposits within the Conard fissure. If one looks in the original publication of Conard Fissure by Barnum Brown, one will find Vespertilio fuscus and Myotis subulatus, but both of those names have been changed in the intervening 110 years, to Eptesicus fuscus and Myotis leibii.

Monday Mysteries

It is long past time I resurrected Monday Mystery fossils. So to celebrate the season, here is a little animal whose relatives, or at least representations thereof, shall be widely seen over the next month.

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If you think you know what this is, please leave your identification in the comments. I will let everyone know what it is and where fossils like this have been found in Arkansas on Friday. Have a great October!

Prehistoric Shark Week, Day 5: From Whence the Great White?

Greetings and welcome to the final day of Prehistoric Shark Week! All week we have covered sharks that swam in Arkansas during the Cretaceous Period. The dinosaurs get all the press, but we had a diverse marine ecology during that time. Last week, we met a few of the non-shark denizens, such as mosasaurs, elasmosaurs, and more. This week, we have seen nurse sharks, goblins, sand tigers, and an array of rays, skates, and angel sharks. We wrap up the festival of marine animals with the question that everyone wants to know. Where did the most famous sharks of all time, the Great White and Megalodon, come from and how does Arkansas play into this?

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A collection of galeomorph sharks that made their home in Cretaceous Arkansas and much of the world’s oceans, appropriately scaled.

The Great White, or simply White Shark, is named Carcharodon carcharias, meaning sharp tooth pointer, although more popularly named for its white belly, is well known as the largest living predatory fish in the sea, reaching up to and, probably over, 20 feet. Megalodon, listed either as Carcharocles megalodon or Carcharodon megalodon, depending on whether or not one believes it is directly related to or convergent with White Sharks, is the largest known predatory fish ever, reaching sizes up to three times that of the White Shark. It appeared in the fossil record about 16 Mya, but went extinct 1.6 Mya (contrary to what a fictitious documentary on the Discovery Channel claimed).

During the Cretaceous, the southwestern part of the state was covered by the Western Interior Seaway, which for us, was essentially equated to having the Gulf coast not just on our doorstep, but flooding it. Those waters were warm, rich in nutrients, and a hotbed of marine life. In those waters, a few sharks of interest made their home.

All of the sharks we will be talking about are lamniform sharks. These sharks are known for being at least partially endothermic, meaning they used their core muscles to create their own heat and maintain an elevated body temperature, giving them the ability to be active hunters even in cooler waters. Of course, it also meant they were hungrier, needing more food, keeping them always on the prowl. This is what allows the White to be such a fearsome hunter today, giving it the power and energy to breach completely out of the water during attacks.

Squalicorax is an extinct shark of the time that is commonly thought to have resembled Whites. These sharks got up to five meters, although they were typically around two meters. Squalicorax is also called the Crow Shark, which some people have speculated it got that name from evidence of its scavenging. However, squalus means shark (and is the scientific genus name for dogfish) and corax means crow, so the name Squalicorax literally means crow shark. Squalicorax_pristodontus_Agassiz,_1843_1Now as to why it was named that way to begin with, no one knows because when Agassiz named it in 1843, he didn’t leave a record as to why. They hunted and scavenged a wide range of animals, everything from turtles to mosasaurs. Unfortunately, the relationships between Squalicorax and other lamnids is uncertain, so whether or not it could have been ancestral to anything, much less Whites or megalodons, is unknown at present.

Another candidate is a shark named Isurus hastalis, an Oligocene shark that lived 30 Mya. Isurus also includes the modern day mako shark. However, a researcher by the name of Mikael Siverson concluded that the Isurus teeth were not makos, but worn down teeth similar to modern Whites. So he changed the name to Cosmopolitodus. It has also been suggested that these sharks originated from a shark called Isurolamna, which lived in the paleocene 65-55 Mya.

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Possible evolutionary sequence of the Great White. http://www.elasmo-research.org

A more recent view, and one which I back (with freely admitted bias because it allows me to say they evolved from Arkansas sharks:) ), is that both Whites and megolodons evolved from an extinct lamnid called Cretolamna, the Cretaceous lamna. This shark had large, strong teeth and was very successful. It had a worldwide distribution and lived from the Cretaceous to the Paleocene. Cretolamna fossils have not been reported in Arkansas thus far, but they were a member of the family Cretoxyrhinidae, of which the shark Serratolamna was a member. The teeth of Cretolamna and Serratolamna are extremely similar, as one might expect from genera in the same family. However, Serratolamna teeth have serrations and Cretolamna does not, making Serratolamna teeth closer in shape to the White Shark. Serratolamna did not have the same worldwide distribution and did not last as long as long as Cretolamna, though. It is impossible to tell which one was directly ancestral to the later sharks, but Cretolamna, due to its more cosmopolitan range, has gotten the nod. It was named first and is much better known than Serratolamna, giving it an edge when people find and identify fossil shark teeth. Thus, it is not a big stretch to say that Serratolamna, or a very close relative, eventually evolved into Carcharodon carcharias as well as Carcharocles (or Carcharodon) megalodon.

Cretoxyrhinidae_-_Serratolamns_gasfana

Serratolamna gafsana. Wikipedia. Photo by Hectonichus.

I hoped you have enjoyed Prehistoric Shark Week and the previous week of Cretaceous Arkansas marine predators. Let me know if there is another group that you think deserves special consideration for a celebratory week.

Day 4 of Prehistoric Shark Week: Sand Tigers

For Day 4 of Prehistoric Shark Week, I would like to mention another modern day shark that has been around since the Cretaceous: the sand tiger sharks. Tomorrow, I will discuss a couple of Cretaceous sharks that may be the ancestors of the two most famous sharks in the world – the Great White and the giant Megalodon.

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Carcharias taurus. Wikipedia. Amada44.

carchariasThe Sand tiger is a common shark in the Cretaceous sediments, or at least, their teeth are, which means they were probably pretty common back then.  The teeth tend to be long and thin, with two small cusps on either side of the large, center blade. Elasmo-branch.org reports that the center blade is smooth-edged with a strongly bilobed root, large bulge in the center of the root (aka lingual protruberance), and nutrient foramen in the center.

There are actually two sharks that are often called sand tigers in the Cretaceous rocks. One is Carcharias holmdelensis, the Cretaceous version of Carcharias taurus, the modern day sand tiger shark. Also going by the name grey nurse shark, amid several others, sand tigers are large-bodied sharks that will eat pretty much anything, but since it is a fairly slow and placid shark most of the time, it doesn’t seem to go after anything that requires a lot of effort. They are known for gulping air to allow themselves to float in the water column without expending much effort. So although they look scary, they appear to be too lazy to live up to appearances.

Smalltooth-sand-tiger-shark-portrait

Odontaspis ferox

The other shark that gets called a sand tiger, is Odontaspis aculeatus, one of the ragged toothed sharks, which also go by the name sand tiger. These sharks were until recently in the same family as Carcharias, but have since been pulled out into their own family. They are very similar, as one might has guessed from the numerous times these sharks have been grouped and split over the years. As Elasmo-research.org put it, “Chaos reigned until Leonard Compagno examined museum specimens from all over the world, corrected misidentifications and sorted out synonyms.”

 

Prehistoric Shark Week, Day 3: Flat Fish

For Day 3 (a little late, yes) of Prehistoric Shark Week, I want to bring to your attention the diversity of chondrichthyans that have opted for a flatter bauplan.

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Ray tooth

Sharks are generally split into two groups, the galeomorphs, which are mostly the more typical torpedo-shaped sharks, including the sharks that most people think of when they envision a shark. The other group is the squalimorphs. These sharks lack an anal fin and many of them have developed a penchant for flatter bodies and broad pectoral fins, and in some cases pelvic fins as well (although not all, such as the dogfish and frilled sharks). Up until recently, the batoids, otherwise known as skates and rays, were considered part of this group, the consensus being that they were a more specialized type of squalimorph shark that had taken flat to an extreme. But the most recent molecular studies have indicated that they are a group unto themselves. The batoids have a long fossil history, with a number of ray teeth found in the Cretaceous deposits of Arkansas, particularly the eagle ray family Myliobatidae. Their teeth are typically flat rectangles on top with a comb-like surface below. Another type of ray that can be found are the guitarfish, or Rhinobatos casieri. These pectoral fins of these fish extend to their head, giving them a triangular shaped front end of a more traditional shark-like back end.

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Shark classification. 

http://www.mesa.edu.au/seaweek2005/pdf_senior/is02.pdf

 

Skates and rays are generally very docile and would not be very threatening, spending their time scrounging about on the sea floor for benthic (living in or on the sea floor) invertebrates and the occasional fish. The same can’t be said for the last member of this group, the sawfish. Armed with a rostrum (its elongated snout) with teeth out to the side, the fish looks like it has a chain saw for a nose. The sawfish will swim into a school of fish and thrash its rostrum rapidly back and forth, spearing and stunning several fish, which it can then gobble up. They can also use it to dig up clams and crabs from the sediment. While they won’t attack humans, any human who provoked one may easily wind up perforated by the rostrum, probably not deadly but certainly painful. Most modern sawfish reach a respectable two meters, but the largest species, the green sawfish (Pristis zijsron) can top seven meters (24 feet). This is as large as the Cretaceous versions. Modern sawfish are typically put into the family Pristiformes. The Cretaceous ones are in their own family, called Sclerorhynchiformes and are not directly related, in that the Cretaceous ones are not thought to be ancestral to the modern ones. They are both put into the group Pristirajea, so they are thought to at least be related. But with the uncertainties in the relationships of the modern fish, the relationships with fossil forms are necessarily less certain. In any case, Arkansas sports several different species from this group, including Schizorhiza stromeri, Sclerorhynchus sp., Ischyrhiza mira, Ischyrhiza avonicola, and Ptychotrygon vermiculata. We were postively awash in sawfish.

Onchopristis numidus black JCS

Onchopristis. Cretaceous. Sawfishconservationsocietyblogspot.com

The true squalimorph sharks that have shown up in the Arkansas Cretaceous rocks are best represented by the Angel shark (Squatina hassei), which looks like an early rendition of a skate, so it is little wonder that most researchers viewed skates and rays as simply more specialized versions of these sharks. Nevertheless, it appears this is case of convergence, not homology (similarity due to relationship). If it is homologous, it isn’t directly so. It is possible both groups had a common slightly flattened ancestor and each took their own route from there.

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Rhinobatos hakelensis. Cretaceous guitarfish. Fossilmuseum.net

All of these fish are pretty docile hunters, scrounging around the sea floor for benthic organisms, all those animals that make their home in or on the sea floor sediments. They spend their time digging around the sand for crabs, clams, and other invertebrates, the occasional fish. When threatened by the presence of a predator, they hide on the bottom, using their shape to help them blend in with the seafloor. Neither the ones today or the ones in the Cretaceous would have bothered a human swimming around them.

Becker, Martin A., Chamberlain, John A., Wolp, George E. 2006. Chondricthyans from the Arkadelphia Formation (Upper Cretaceous: Upper Maastrichtian) of Hot Spring County, Arkansas

 

 

Prehistoric Shark Week, Day 2: Goblins

For Day 2 of Prehistoric Shark Week on paleoaerie, we are going to take a look at my personal favorite shark. In the late Cretaceous, it was called Scapanorhynchus, the spade snout. But its closest living relative is called Mitsukurina owstoni, also known as the goblin shark. The perfect shark for Halloween.

Scapanorhynchus.jpg

Scapanorhynchus lewisii. Wikipedia

Scapanorhynchus means spade snout, so named for the elongated, flat snout, the same feature which got the modern shark named goblin. Most of them are small, less than one meter, but can get in excess of four meters. Spade snouts were some of the earliest sharks in Neoselachii, the modern sharks. One of the things this means is that they did not just have straight cartilaginous skeletons, they calcified most parts of the skeleton to reinforce the cartilage. They didn’t make true bone, but the calcium spicules provided more strength for the cartilage.

 

Scapanorhynchus (1)

Scapanorhynchus texanus. http://www.njfossils.net/goblin

220px-ScapanorhynchusCretaceousIsraelTwoGoblin shark teeth are long and thin, looking like a mouth full of curved needles. But what most people are fascinated by is the amazing length to which they can protrude their jaws. Modern sharks have what is known as hyostylic jaws, meaning that the jaws are not directly connected to the skull. Instead, they are attached at the back of the jaws on an intermediary bone that allows the jaw to swing forward. All sharks can do this to an extent, but the goblin shark is expecially known for it.

The modern goblin sharks are generally only found in deep water. Its Cretaceous cousins, on the other hand, were widespread in shallow marine areas. Like many fish in the Cretaceous, they seem to have survived the mass extinction even at the end of the Mesozoic by going deep.

Prehistoric Shark Week

This week we will celebrate fossil sharks of the Mesozoic that have been found in Arkansas. Because all of our surface rocks of the period are from the Cretaceous, the sharks are limited to that time. There are other cool sharks from the Paleozoic, but they will have to wait for another time. Hunting for shark teeth in Arkansas can best be done in the chalk formations called the Annona and Saratoga in southwest Arkansas. But you can also find them in several other formations as well.

Many of the sharks found in the Cretaceous in Arkansas have contemporary species. While the species may vary, the genus name is very long-lived. For those who are unaware, scientific names follow a binomial system, with a genus and a species name, the genus being the first name and indicating a group of very closely related species. It is next to impossible to tell the difference between species of sharks just by their teeth unless, and many times even if, one is an expert, so I will be sticking with the genus names.

To begin the week, I present to you Ginglymostoma, the nurse shark.

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The scientific name comes from the shape of its mouth. The origin of the name nurse shark is not clear, but it is considered likely to have originated with the Old English word Hurse, for sea floor shark.

Known for its puckered mouth and barbels on the sides of its mouth, nurse sharks spend most of their time near the sea floor scrounging for whatever small animal they can catch. They are very docile and will only bite if provoked. Humans are far too big for nurse sharks to be interested in, so unless one really goes out of their way to annoy a nurse shark, you’re pretty safe, even from the largest ones, which can get over 4 meters.

Nurse-shark-swimming